Late onset pulmonary complications (bronchiolitis obliterans and interstitial pneumonia) are a significant cause of morbidity and mortality after bone marrow transplantation. Their development correlates with a switch" in immune phenotype. Using a murine model of lung disease following allogeneic bone marrow transplantation we will test the hypothesis that regulatory CD8+ lymphocytes mediate the development of chronic pulmonary graft versus host disease after bone marrow transplantation. We hypothesize regulatory CD8+ lymphocytes are initially alloimmune cytotoxic T lymphocytes and after multiple rounds of antigenic stimulation become anergic, develop regulatory properties and functionally suppress the TH1 response leading to chronic disease. The specific aims include: 1)To determine the impact of pulmonary chimerism in generating an alloimmune response in the lung after bone marrow transplant in a murine model, 2)To determine if CD8+ regulatory cells can be manipulated to effect a decrease in GVHD and late onset lung disease in a murine model, 3)To identify the mechanisms by which CD8+ regulatory cells suppress the alloimmune response, and 4)To prospectively study a cohort of patients after non-myeloablative transplantation. This proposal describes a 5 year training program to develop an academic career in basic science research in transplant immunology as it relates to pulmonary complications of bone marrow transplantation. The principal investigator has completed a pulmonary/critical care fellowship training program where she learned basic pulmonary immunology in human subjects. This proposal outlines training to expand upon these basic techniques and extend them to a murine model, under the mentorship of Dr. David Wilkes, an expert in pulmonary transplant immunology. Training in hematopoietic stem cell transplantation will be provided by Dr. Mary Dinauer and Dr. Edward Srour, experts in cell trafficking and murine bone marrow transplantation.